1. Field of the Invention
The present invention relates to a roll-off reducing agent. More specifically, the present invention relates to a roll-off reducing agent composition comprising the roll-off reducing agent, a process of reducing roll-off of a polished substrate by applying the roll-off reducing agent to the substrate, a process for producing a polished substrate by applying the roll-off reducing agent to the substrate, a polishing composition, a polishing process of a substrate to be polished by applying the polishing composition to the substrate, and a process for producing a substrate by applying the polishing composition to a substrate to be polished.
2. Discussion of the Related Art
Over the years, a demand for a technique for further increasing the capacity of the hard discs has become greater. As a leading means for increasing the capacity of the hard discs, there has been considered a means of producing a substrate capable of recording data even to its outer periphery by reducing roll-off (edge rounding of end side of a substrate) caused in the polishing process. For instance, various mechanical polishing conditions which can reduce roll-off, such as making a polishing pad more rigid, and making a polishing load smaller, have been studied. However, although a certain extent of an effect is obtained for reducing roll-off by these mechanical polishing conditions, the effect has not yet been satisfactory.
In addition, as a polishing composition capable of reducing roll-off, a composition comprising water, α-alumina particles and aluminum nitrate has been known (Japanese Patent Laid-Open No. Hei 9-286975). However, this composition does not have a satisfactory effect of reducing roll-off, and studies of the polishing components having an excellent effect for reducing roll-off have not yet been sufficiently made at present.
On the other hand, the hard discs have been greatly developed over the years in the trends of miniaturization and high capacity, so that the trend of high density has been progressed, that the minimum recording area has become smaller, and that the floating amount of a magnetic head has been made increasingly smaller. Therefore, there have been desired to increase the polishing rate and reduce the surface roughness, and to reduce surface defects such as scratches and pits in the polishing process of a hard disc substrate. In view of this, there have been studied on a polishing composition by using water, alumina, boehmite and a chelating compound (Japanese Patent Laid-Open No. Hei 11-92749, and the like); a polishing composition comprising water, α-alumina, and an alumina sol stabilized with acetic acid (Japanese Patent Laid-Open No. 2000-63805); a polishing composition for an aluminum magnetic disc, comprising water, an alumina abrasive powder, a polishing accelerator such as gluconic acid or lactic acid, and a surface-modifying agent such as a colloidal alumina (Japanese Patent Laid-Open No. Hei 2-84485); a polishing composition comprising water, an alumina abrasive, and a polishing accelerator comprising molybdic acid and an organic acid (Japanese Patent Laid-Open No. Hei 7-216345); and a polishing process.
However, none of these polishing compositions sufficiently satisfy all of an effect of reducing roll-off, an effect of increasing the polishing rate, an effect of reducing the surface roughness of a polished object, and an effect of reducing surface defects such as scratches and pits. Therefore, a polishing composition having further enhanced effects is in demand.
An object of the present invention is to provide a roll-off reducing agent capable of reducing roll-off of a polished substrate caused by polishing, and increasing a polishing rate; a roll-off reducing agent composition comprising the roll-off reducing agent; a process of reducing roll-off of a polished substrate by using the roll-off reducing agent; and a process for producing a polished substrate by using the roll-off reducing agent.
Also, another object of the present invention is to provide a polishing composition having an increased polishing rate, and a reduced surface roughness without causing a surface defect on the surface of the polished substrate, and being capable of reducing roll-off; a polishing process of a polished substrate by using the polishing composition; and a process for producing a polished substrate.
These and other objects of the present invention will be apparent from the following description.
In the present specification, the term “roll-off” refers to a state so-called edge rounding of an end surface, in which a part of an end surface of a substrate to be polished is more largely grinded as compared to that of the central part, thereby rounding off the end part.